Lithium supplement diaphragm, preparation method thereof and lithium ion battery

文档序号：881063 发布日期：2021-03-19 浏览：27次中文

阅读说明：本技术 一种补锂隔膜及其制备方法与锂离子电池 (Lithium supplement diaphragm, preparation method thereof and lithium ion battery ) 是由宋佳宜杜双龙熊后高兰枭周伟吕正中于 2020-12-14 设计创作，主要内容包括：本发明提供一种补锂隔膜及其制备方法与锂离子电池,所述制备方法包括以下步骤：(1)将两条隔膜对称贴合,得到双层隔膜；(2)将步骤(1)所得双层隔膜的两侧表面分别贴合锂带,得到复合隔膜；(3)将步骤(2)所得复合隔膜进行辊压并切割,得到补锂隔膜。本发明提供的制备方法提升了操作的安全性,降低了生产成本,避免了铝箔氧化与负极片在复合过程中的掉料现象。(The invention provides a lithium-supplementing diaphragm, a preparation method thereof and a lithium ion battery, wherein the preparation method comprises the following steps: (1) symmetrically attaching the two diaphragms to obtain a double-layer diaphragm; (2) respectively attaching lithium belts to the surfaces of two sides of the double-layer diaphragm obtained in the step (1) to obtain a composite diaphragm; (3) and (3) rolling and cutting the composite diaphragm obtained in the step (2) to obtain the lithium supplement diaphragm. The preparation method provided by the invention improves the operation safety, reduces the production cost and avoids the phenomenon of material dropping in the process of compounding the aluminum foil with the negative plate.)

1. The preparation method of the lithium-supplementing separator is characterized by comprising the following steps:

(1) symmetrically attaching the two diaphragms to obtain a double-layer diaphragm;

(2) respectively attaching lithium belts to the surfaces of two sides of the double-layer diaphragm obtained in the step (1) to obtain a composite diaphragm;

(3) and (3) rolling and cutting the composite diaphragm obtained in the step (2) to obtain the lithium supplement diaphragm.

2. The preparation method according to claim 1, wherein the separator in step (1) comprises a ceramic layer and a separator layer which are stacked, and the ceramic layers of the two separators are symmetrically attached;

preferably, the material of the membrane layer includes polyethylene and/or polypropylene.

3. The production method according to claim 1 or 2, wherein the thickness of the separator in step (1) is 10 to 50 μm;

preferably, the porosity of the separator of step (1) is 20 to 40%.

4. The method according to any one of claims 1 to 3, wherein the lithium ribbon of step (2) is provided with at least 1 lithium foil arranged in parallel;

preferably, the lithium foil is attached to the double-layer separator;

preferably, the lithium foil has a thickness of 3 to 7 μm;

preferably, the width of the lithium foil is 3-5 mm.

5. The method of claim 4, wherein the lithium foil is a porous structure;

preferably, the pore size of the porous structure is 0.1-10 μm;

preferably, the lithium foil has a porosity of 10-30%.

6. The manufacturing method according to any one of claims 1 to 5, wherein a PET film is respectively attached to both side surfaces of the composite separator before the rolling in step (3);

preferably, the number average molecular weight of the polyethylene terephthalate in the PET film is 150000-.

7. The production method according to any one of claims 1 to 6, wherein the pressure for the rolling in step (3) is 200-400 MPa.

8. The method of any one of claims 1 to 7, comprising the steps of:

(1) symmetrically attaching two diaphragms with the thickness of 10-50 mu m and the porosity of 20-40% to obtain a double-layer diaphragm; the diaphragm comprises ceramic layers and diaphragm layers which are arranged in a stacked mode, the ceramic layers of the two diaphragms are symmetrically attached to each other, and the material of the diaphragm layers comprises polyethylene and/or polypropylene;

(2) respectively attaching lithium belts to the surfaces of two sides of the double-layer diaphragm obtained in the step (1) to obtain a composite diaphragm; the lithium strip is provided with at least 1 lithium foil arranged in parallel, the lithium foil is attached to the double-layer diaphragm, the thickness of the lithium foil is 3-7 mu m, and the width of the lithium foil is 3-5 mm; the lithium foil is of a porous structure, the aperture of the porous structure is 0.1-10 mu m, and the porosity of the lithium foil is 10-30%;

(3) and (3) respectively attaching PET films to the two side surfaces of the composite diaphragm obtained in the step (2), wherein the number average molecular weight of the polyethylene glycol terephthalate in the PET films is 150000-1500000, and rolling and cutting are carried out under the pressure of 200-400MPa to obtain the lithium-supplement diaphragm.

9. The lithium supplement diaphragm is characterized by comprising a diaphragm and a lithium belt which are arranged in a stacked mode.

10. A lithium ion battery, characterized in that the lithium ion battery comprises a positive plate, a negative plate, an electrolyte and the lithium-supplementing separator of claim 9.

Technical Field

The invention belongs to the technical field of lithium ion batteries, relates to a lithium supplement diaphragm, and particularly relates to a lithium supplement diaphragm, a preparation method of the lithium supplement diaphragm and a lithium ion battery.

Background

In recent years, new energy automobiles are abnormally exploded to promote explosive growth of the domestic power battery industry, and power batteries are taken as the core of electric automobiles and mainly divided into lithium iron phosphate batteries and ternary lithium batteries. Compared with a ternary lithium battery, the lithium iron phosphate battery has greater advantages in safety. This is because the P — O bond in the lithium iron phosphate crystal is stable and hard to decompose, and does not collapse and generate heat or form a strongly oxidizing substance like lithium cobaltate even at high temperature or at overcharge, thereby having excellent safety.

In order to further break through the electrical property of the lithium iron phosphate battery, in recent years, experimenters propose a means for supplementing lithium to a negative plate, so as to supplement irreversible capacity loss of the negative plate in the first charging, thereby achieving the purpose of improving the first coulombic efficiency. The conventional method for supplementing lithium to the negative electrode directly adopts metal Li to supplement lithium, and has the advantages of high lithium supplementing efficiency, no residue after reaction, high activity of the metal Li, high requirement on environmental control, large-scale equipment, high cost investment and complex improvement on the conventional production process. Meanwhile, the adoption of metal Li has a great safety risk, and particularly, the suspension of metal Li powder in the air can cause dust explosion.

CN 110676427a discloses a lithium ion battery negative electrode material lithium supplementing method and a battery preparation method, the preparation method comprises the following steps: s1, coating the negative electrode slurry on a negative electrode current collector, and rolling to prepare a negative electrode sheet; and S2, pressing the cathode plate prepared in the step S1 with the surface passivated lithium belt to obtain the composite cathode plate. Compared with the prior art, the lithium ion battery has the advantages that the metal lithium with active property is passivated and stabilized, the negative plate and the lithium belt are tightly compounded by controlling the pressing pressure, so that enough lithium source is ensured to supplement lithium ions consumed by side reactions, the SEI film is continuously increased and repaired and the like in the subsequent circulation process, and the circulation performance of the battery is improved. However, the composite negative electrode sheet has the possibility of material falling in the rolling process, and still has a large modification space.

CN 109728306a discloses a lithium-supplementing negative plate and a preparation method thereof, where the lithium-supplementing negative plate includes a negative current collector, a first negative slurry layer disposed on two surfaces of the negative current collector, a lithium foil layer closely attached to the surface of the first negative slurry layer, and a second negative slurry layer disposed on the surface of the lithium foil layer. Compared with the prior art, the invention realizes the effect of lithium supplement on the negative plate, improves the first efficiency and the cycle performance of the battery, and simultaneously adds the second negative slurry layer on the surface of the lithium foil layer, thereby avoiding the lithium foil layer from being exposed in the air and reducing the requirement of production conditions. However, the lithium foil layer in the invention is easily oxidized when being contacted with moisture in the slurry in the second negative electrode slurry coating process, and the lithium-supplement negative electrode sheet has the risk of material dropping after being compounded.

CN 107768743a discloses a lithium ion battery lithium supplementing method, in which positive and negative electrode plates and porous lithium foil are laminated or wound in the order of positive electrode | diaphragm | porous lithium foil | diaphragm | negative electrode to make a battery with a third electrode (lithium supplementing electrode) in addition to the positive electrode and the negative electrode. The lithium supplementing method can accurately control the lithium supplementing amount and the lithium supplementing time, improves the lithium supplementing uniformity, avoids the local lithium precipitation phenomenon, and improves the first coulombic efficiency, the energy density and the cycle life of the lithium ion battery. However, the invention has low practicability because the impedance between the positive electrode and the negative electrode is increased and the amount of the diaphragm is increased.

Therefore, how to provide a method for supplementing lithium to a negative electrode, which improves the operation safety, reduces the production cost, and avoids the material dropping phenomenon of aluminum foil oxidation and a negative electrode plate in the compounding process becomes a problem to be solved urgently by technical personnel in the field at present.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a lithium supplement diaphragm, a preparation method thereof and a lithium ion battery.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a method for preparing a lithium-doped separator, comprising the steps of:

(1) symmetrically attaching the two diaphragms to obtain a double-layer diaphragm;

(2) respectively attaching lithium belts to the surfaces of two sides of the double-layer diaphragm obtained in the step (1) to obtain a composite diaphragm;

(3) and (3) rolling and cutting the composite diaphragm obtained in the step (2) to obtain the lithium supplement diaphragm.

According to the invention, two lithium supplement diaphragms are simultaneously prepared by the preparation method, so that the production efficiency is improved.

Compared with the method of directly placing the lithium foil on the surface of the negative electrode coating to prepare the composite negative electrode plate, the preparation method avoids the material falling phenomenon in the rolling process, and compared with the moisture in the negative electrode coating, the moisture on the surface of the diaphragm is easier to dry out, namely the moisture content of the diaphragm is lower, so that the oxidation influence on the lithium foil is smaller. In addition, compared with the lithium powder adopted by the traditional negative electrode lithium supplement, the preparation method has the advantages that the safety and the convenience of the lithium foil are higher, the requirement on production equipment is low, and the production cost is reduced.

Preferably, the separator in step (1) includes a ceramic layer and a separator layer which are stacked, and the ceramic layers of the two separators are symmetrically attached.

Preferably, the material of the membrane layer includes polyethylene and/or polypropylene.

According to the invention, the ceramic layer can improve the high-temperature resistance of the diaphragm, and prevent the diaphragm from deforming or being damaged in a long-time high-temperature working environment, thereby influencing the electrical property and the safety performance of the battery.

Preferably, the thickness of the separator in step (1) is 10 to 50 μm, and may be, for example, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm, but is not limited to the values listed, and other values not listed in the range of the values are also applicable.

Preferably, the porosity of the separator in step (1) is 20-40%, for example, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38% or 40%, but is not limited to the recited values, and other values not recited in the range of the recited values are also applicable.

In the invention, the porosity of the diaphragm in the step (1) has certain influence on the electrical property of the battery, and when the porosity of the diaphragm is less than 20%, the smooth transmission of ions is not facilitated, so that the first coulomb efficiency of the battery is reduced; when the porosity of the separator is greater than 40%, the battery is easily short-circuited.

Preferably, at least 1 lithium foil arranged in parallel, such as 1, 2, 3, 4 or 5, is disposed on the lithium ribbon in step (2), but not limited to the values listed, and other values not listed in the range of the values are also applicable.

Preferably, the lithium foil conforms to the double layer separator.

In the invention, the number of the lithium foils arranged on the lithium strip determines the lithium supplement amount of the lithium supplement diaphragm.

Preferably, the lithium foil has a thickness of 3 to 7 μm, and may be, for example, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm or 7 μm, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the lithium foil has a width of 3 to 5mm, and may be, for example, 3mm, 3.2mm, 3.4mm, 3.6mm, 3.8mm, 4mm, 4.2mm, 4.4mm, 4.6mm, 4.8mm or 5mm, but is not limited to the recited values, and other values not recited within the range of values are equally applicable.

Preferably, the lithium foil is of a porous structure.

Preferably, the pore size of the porous structure is 0.1-10 μm, and may be, for example, 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, but is not limited to the recited values, and other values not recited within the range of values are equally applicable.

Preferably, the lithium foil has a porosity of 10-30%, for example 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28% or 30%, but is not limited to the recited values, and other values not recited within the range of values are equally applicable.

Preferably, the PET films are respectively attached to both side surfaces of the composite separator before the rolling in the step (3).

Preferably, the number average molecular weight of the polyethylene terephthalate in the PET film is 150000-1500000, such as 150000, 300000, 500000, 700000, 900000, 1100000, 1300000 or 1500000, but is not limited to the recited values, and other non-recited values within the range of the values are also applicable.

According to the invention, the PET film can prevent the composite diaphragm from being damaged due to contact friction between the composite diaphragm and a roller in a rolling process.

Preferably, the rolling pressure in step (3) is 200-400MPa, such as 200MPa, 220MPa, 240MPa, 260MPa, 280MPa, 300MPa, 320MPa, 340MPa, 360MPa, 380MPa or 400MPa, but not limited to the values listed, and other values not listed in the range are also applicable.

As a preferred technical solution of the first aspect of the present invention, the preparation method comprises the steps of:

In a second aspect, the present invention provides a lithium replenishment separator comprising a separator and a lithium ribbon arranged in a stacked arrangement.

In a third aspect, the present invention provides a lithium ion battery, which includes a positive plate, a negative plate, an electrolyte and the lithium supplement diaphragm according to the second aspect.

In the present invention, the positive plate, the negative plate and the electrolyte are conventionally used by those skilled in the art, and only the positive plate needs to be ensured to be a lithium iron phosphate positive plate, so that the positive plate, the negative plate and the electrolyte are not particularly limited herein, for example, the positive plate, the negative plate and the electrolyte disclosed in the first embodiment of CN 110556582a may be used.

In the present invention, the assembly method of the lithium ion battery is a conventional technical means, as long as the positive plate, the negative plate, the electrolyte and the lithium-supplement diaphragm can be assembled into the lithium ion battery, the lithium foil layer of the lithium-supplement diaphragm is attached to the negative plate, and the ceramic layer of the lithium-supplement diaphragm is attached to the positive plate, so the assembly method is not particularly limited, and for example, the assembly method disclosed in the embodiment one of CN 110690506a can be adopted.

Compared with the prior art, the invention has the beneficial effects that:

(1) compared with the method for preparing the composite negative plate by directly placing the lithium foil on the surface of the negative coating, the method provided by the invention avoids the phenomenon of material falling in the rolling process, and compared with the moisture in the negative coating, the moisture on the surface of the diaphragm is easier to dry out, namely the moisture content of the diaphragm is lower, so that the oxidation influence on the lithium foil is smaller, the electrical property of the battery is further improved, and the first coulomb efficiency of the battery reaches 93% or more and can reach 98% to the maximum extent;

(2) compared with the lithium powder adopted by the traditional negative electrode lithium supplement, the preparation method provided by the invention has the advantages that the safety and the convenience of the lithium foil are higher, the requirement on production equipment is low, and the production cost is reduced.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments.

Example 1

The embodiment provides a lithium-supplementing diaphragm and a preparation method thereof, wherein the preparation method comprises the following steps:

(1) symmetrically attaching two diaphragms with the thickness of 30 micrometers and the porosity of 30% to obtain a double-layer diaphragm; the diaphragm comprises ceramic layers and diaphragm layers which are arranged in a stacked mode, the ceramic layers of the two diaphragms are symmetrically attached to each other, and the diaphragm layers are made of polyethylene;

(2) respectively attaching lithium belts to the surfaces of two sides of the double-layer diaphragm obtained in the step (1) to obtain a composite diaphragm; the lithium strip is provided with 2 lithium foils arranged in parallel, the lithium foils are attached to the double-layer diaphragm, the thickness of each lithium foil is 5 micrometers, and the width of each lithium foil is 4 mm; the lithium foil is of a porous structure, the aperture of the porous structure is 5 microns, and the porosity of the lithium foil is 20%;

(3) and (3) respectively attaching PET (polyethylene terephthalate) films to the two side surfaces of the composite diaphragm obtained in the step (2), wherein the number average molecular weight of the polyethylene terephthalate in the PET films is 800000, and rolling and cutting the PET films under the pressure of 300MPa to obtain the lithium-supplement diaphragm.

Example 2

The embodiment provides a lithium-supplementing diaphragm and a preparation method thereof, wherein the preparation method comprises the following steps:

(1) symmetrically attaching two diaphragms with the thickness of 20 mu m and the porosity of 25% to obtain a double-layer diaphragm; the diaphragm comprises ceramic layers and diaphragm layers which are arranged in a stacked mode, the ceramic layers of the two diaphragms are symmetrically attached to each other, and the diaphragm layers are made of polypropylene;

(2) respectively attaching lithium belts to the surfaces of two sides of the double-layer diaphragm obtained in the step (1) to obtain a composite diaphragm; the lithium belt is provided with 3 lithium foils arranged in parallel, the lithium foils are attached to the double-layer diaphragm, the thickness of each lithium foil is 4 micrometers, and the width of each lithium foil is 3.5 mm; the lithium foil is of a porous structure, the aperture of the porous structure is 2.5 mu m, and the porosity of the lithium foil is 15%;

(3) and (3) respectively attaching PET (polyethylene terephthalate) films to the two side surfaces of the composite diaphragm obtained in the step (2), wherein the number average molecular weight of polyethylene terephthalate in the PET films is 450000, and rolling and cutting the PET films under the pressure of 250MPa to obtain the lithium-supplement diaphragm.

Example 3

The embodiment provides a lithium-supplementing diaphragm and a preparation method thereof, wherein the preparation method comprises the following steps:

(1) symmetrically attaching two diaphragms with the thickness of 40 mu m and the porosity of 35 percent to obtain a double-layer diaphragm; the diaphragm comprises ceramic layers and diaphragm layers which are arranged in a stacked mode, the ceramic layers of the two diaphragms are symmetrically attached to each other, and the diaphragm layers are made of polyethylene;

(2) respectively attaching lithium belts to the surfaces of two sides of the double-layer diaphragm obtained in the step (1) to obtain a composite diaphragm; 1 lithium foil is arranged on the lithium strip, the lithium foil is attached to the double-layer diaphragm, the thickness of the lithium foil is 6 micrometers, and the width of the lithium foil is 4.5 mm; the lithium foil is of a porous structure, the aperture of the porous structure is 7.5 mu m, and the porosity of the lithium foil is 25%;

(3) and (3) respectively attaching PET films with the number average molecular weight of 1150000 to the two side surfaces of the composite diaphragm obtained in the step (2), rolling and cutting under the pressure of 350MPa to obtain the lithium supplement diaphragm.

Example 4

The embodiment provides a lithium-supplementing diaphragm and a preparation method thereof, wherein the preparation method comprises the following steps:

(1) symmetrically laminating two diaphragms with the thickness of 10 mu m and the porosity of 20 percent to obtain a double-layer diaphragm; the diaphragm comprises ceramic layers and diaphragm layers which are arranged in a stacked mode, the ceramic layers of the two diaphragms are symmetrically attached to each other, and the diaphragm layers are made of polypropylene;

(2) respectively attaching lithium belts to the surfaces of two sides of the double-layer diaphragm obtained in the step (1) to obtain a composite diaphragm; the lithium strip is provided with 2 lithium foils arranged in parallel, the lithium foils are attached to the double-layer diaphragm, the thickness of each lithium foil is 3 micrometers, and the width of each lithium foil is 3 mm; the lithium foil is of a porous structure, the aperture of the porous structure is 0.1 mu m, and the porosity of the lithium foil is 10%;

(3) and (3) respectively attaching PET (polyethylene terephthalate) films to the two side surfaces of the composite diaphragm obtained in the step (2), wherein the number average molecular weight of polyethylene terephthalate in the PET films is 150000, and rolling and cutting the PET films under the pressure of 200MPa to obtain the lithium-supplement diaphragm.

Example 5

The embodiment provides a lithium-supplementing diaphragm and a preparation method thereof, wherein the preparation method comprises the following steps:

(1) symmetrically attaching two diaphragms with the thickness of 50 microns and the porosity of 40% to obtain a double-layer diaphragm; the diaphragm comprises ceramic layers and diaphragm layers which are arranged in a stacked mode, the ceramic layers of the two diaphragms are symmetrically attached to each other, and the diaphragm layers are made of polyethylene;

(2) respectively attaching lithium belts to the surfaces of two sides of the double-layer diaphragm obtained in the step (1) to obtain a composite diaphragm; the lithium belt is provided with 3 lithium foils arranged in parallel, the lithium foils are attached to the double-layer diaphragm, the thickness of each lithium foil is 7 micrometers, and the width of each lithium foil is 5 mm; the lithium foil is of a porous structure, the aperture of the porous structure is 10 micrometers, and the porosity of the lithium foil is 30%;

(3) and (3) respectively attaching PET films to the two side surfaces of the composite diaphragm obtained in the step (2), wherein the number average molecular weight of polyethylene glycol terephthalate in the PET films is 1500000, and rolling and cutting the PET films under the pressure of 400MPa to obtain the lithium-supplement diaphragm.

Example 6

This embodiment provides a lithium-doped separator and a method for preparing the same, wherein the preparation method is the same as that of embodiment 1 except that the porosity of the separator is changed to 18%, and thus the details are not repeated herein.

Application example 1

In the application example, the positive plate, the negative plate, the electrolyte and the lithium-supplement diaphragm provided in the embodiment 1 are assembled into the lithium ion battery, the positive plate, the negative plate and the electrolyte are the positive plate, the negative plate and the electrolyte disclosed in the embodiment one in CN 110556582A, and the assembling method is the assembling method disclosed in the embodiment one in CN 110690506 a.